Novel Bacteria in Alaskan Ice May Be 32,000 Years Old

By NICHOLAS WADE

Published: February 26, 2005

NASA researchers say they have recovered bacteria that apparently lay dormant for 32,000 years in a frozen pond in central Alaska.

If confirmed, the finding means that there may be many other pockets of ancient life in permafrost and seafloor sediments. The hardiness of the bacteria also suggests that life could survive even on Mars, in places like the frozen sea reported by other researchers this week.

But the NASA claim was greeted with some reserve by other scientists because previous claims of resuscitating ancient bacteria have not been borne out.

The bacterium, a novel species, was recovered from a frozen pond exposed in the side of the Fox tunnel, a hole dug through Pleistocene-era ice by the Cold Regions Research and Engineering Laboratory at the Army. Dr. Richard B. Hoover, a biologist at NASA's Marshall Space Flight Center, said that while visiting the refrigerated tunnel he noticed a discolored patch in a layer that froze 32,000 years ago, according to radiocarbon data. Taking samples back to his laboratory, Dr. Hoover and his colleague Dr. Elena V. Pikuta noticed bacteria that started moving as soon as the ice thawed.

The bacteria resembled a group of microbes called carnobacteria that can tolerate cold and are often isolated from refrigerated food. The NASA researchers established that the microbes belonged to a new species, which they have named Carnobacterium pleistocenium in honor of its age. The bacterium is not poisonous, Dr. Hoover said, although some of its close relatives cause disease in fish. The researchers are reporting their finding in the International Journal of Systematic and Evolutionary Microbiology.

Dr. Hoover said he believed the bacteria were not able to divide during the eons spent locked in the ice, so the specimens he thawed out would have been 32,000 years old, the time when the Alaskan pond was last in liquid form.

Other researchers said in 2000 that they had resuscitated bacteria 250 million years old from liquid trapped in rocks in Pennsylvania, but the claim was received skeptically by other scientists. One reason is that DNA, the repository of genetic information, is not a fully stable chemical and degrades at such a rate that every cell in the human body loses some 5,000 DNA units a day. During an organism's lifetime, the lost information is mostly restored by a suite of DNA repair enzymes. But as soon as metabolism ceases, so does the repair system, severely limiting how long even a dormant organism can endure.

Some bacteria can form spores, a hunkered-down form that can survive for perhaps a few hundred years. But the Fox tunnel bacteria were not in spore form, Dr. Hoover said.

Dr. Eske Willerslev, an expert on permafrost bacteria at Oxford University in England, said the NASA researchers' find was ''definitely very interesting if it is correct.'' He said it was possible that the Fox tunnel bacteria, though frozen, could still metabolize very slowly, enough to keep their DNA repair kits running. If so, their DNA could have maintained its integrity at least until the cells ran out of locally available nutrients.

But both Dr. Willerslev and Dr. Alan Cooper, professor of ancient biomolecules at Oxford, said they doubted whether the NASA researchers had ruled out all possible sources of contamination with contemporary bacteria. ''I'm pretty suspicious about these claims because it's so easy with microbes to get contamination,'' Dr. Willerslev said.

Dr. Cooper said the Fox tunnel was quite dirty when he visited it and suggested that contemporary bacteria brought in by visitors could have worked their way deep into the ice. He also said it was a standard requirement for a sample being tested for ancient DNA to be split and analyzed in two separate places, to guard against the risk of contamination by bacteria in the laboratory.

In response to these critiques, Dr. Hoover said the Fox tunnel was kept at a constant low temperature without melting, so contemporary bacteria brought into the tunnel could not reach the depth from which he had taken his samples. He said it was unnecessary to analyze the sample in two laboratories because the resuscitated bacterium was a novel species, not one of those commonly found in laboratories.

If ancient bacteria can really survive in permafrost and seafloor sediments, Dr. Willerslev said, that would have ''huge implications'' for evolutionary biology because viable bacteria from previous eras would be able to re-enter the environment of today as their niches became exposed. But more work is needed to establish that bacteria really can survive from distant epochs, he said.

Life is generally regarded as being impossible in the absence of water. But if bacteria like those of the Fox tunnel can survive in ice, that would strengthen the possibility of life existing on Mars.

Dr. Hoover said that some microbes generated antifreeze chemicals that might melt the ice around them and liberate nutrients. The Fox tunnel bacteria demonstrate the possibility of survival in frozen ice, he said, and hence suggest the Martian surface may not be quite as inhospitable to life as it seems.

Photo: Bacteria, viewed by a microscope, believed frozen for 32,000 years. (Photo by Asim Bej/University of Alabama at Birmingham)